1. Field of the Invention
The present invention relates to a wireless access system, and more particularly, to a method for supporting emergency communication in a relay system.
2. Discussion of the Related Art
Hereinafter, a relay station (RS) used in the present invention will be described in brief.
A standardization project of a new title called multi-hop relay is currently in progress in IEEE (Institute of Electrical and Electronics Engineers) 802.16 of 2006 since publications of the standard IEEE 802.16-2004 based on fixed subscriber mobile stations and the standard IEEE 802.16e-2005 for providing mobility of subscriber mobile stations. This standardization project handled by a task group j (IEEE 802.16j) within the IEEE 802.16 has started to discuss usage model, related terminologies, and technical requirements in the second meeting on July of 2006 after the first formal meeting on May of 2006. Hereinafter, the IEEE 802.16 task group j will be abbreviated as “802.16j”.
It is expected that the relay station (RS) will widely be used in a wireless communication system for next generation. Hereinafter, for conciseness of description, the relay station will be described based on the concept of the relay station considered by the IEEE 802.16j. However, the concept of the relay station which will be described hereinafter may be used substantially the same as a relay station considered by a 3GPP IMT-A (LTE-A) system.
Project authorization request (PAR) of 802.16j is intended for two following tasks of the standardization project which will be performed:
1. Coverage extension; and
2. Throughput enhancement.
FIG. 1 is a conceptional view illustrating a multi-hop relay system.
In FIG. 1, a reference numeral 101 denotes a base station, reference numerals 102a to 102d denote relay stations, and reference numerals 103a to 103d denote mobile stations. As illustrated in FIG. 1, signal transfer through the relay stations 102a and 102b can be performed at a zone other than the base station 101. Also, the mobile station 103d located within the zone of the base station 101 is allowed to set a path of high quality, which has an adaptive modulation and coding (AMC) scheme of high level through the relay station 102d, whereby enhancement of system throughput can be obtained through the same radio resource.
Under the rule that the mobile station implemented based on the existing 802.16-2004 specification and the existing 802.16e-2005 specification should perform communication with the relay station without any additional function, it is predicted that the standard specification to be made by the 802.16j project has a limited range in accordance with addition of some function for controlling the relay station to the relay station and the existing base station.
The relay station can be regarded as a subscriber mobile station that performs operations of a physical layer and a media access control (MAC) layer. Also, the relay station is mainly controlled by the base station but may have a predetermined control function if necessary. As usage models currently in discussion, in addition to a fixed relay station, various types of relay stations are considered. Examples of such relay stations include a mobile relay station for temporarily providing a service to a specific zone and a relay station that can be built in cars or subways.
When a mobile station that supports a general multi-hop relay initially enters a network or performs an initial network entry procedure with a base station or a relay station, the base station can determine relay through the relay station.
For example, if a channel status between the base station and the mobile station is greater than a specific reference value, the mobile station may try direct communication with the base station. If the channel status is less than the specific reference value, or if the mobile station cannot receive a signal of the base station and has a good channel status with a neighboring relay station, path to the relay station is set.
However, when the mobile station requests an emergency service while performing an initial network entry procedure for registration with the base station, or when the mobile station requests an emergency service while performing communication with the base station or the relay station, a procedure for connection between the mobile station and a neighboring mobile station is not defined if the channel status between the mobile station and the base station or the relay station is less than the specific reference value.
FIG. 2 is a diagram illustrating an example of an emergency status.
In more detail, FIG. 2 illustrates that a base station (BS), a femto base station (FBS) or a relay station (RS) fails to perform a normal function due to natural disaster or other accident.
Referring to FIG. 2, the mobile station may fail to receive a service from a current serving relay station due to an accident occurring in the relay station. At this time, the mobile station may perform a communication service of an emergency mode by shifting to the emergency mode.